1. Field of the Invention
The present invention relates generally to data processing systems and more paticularly to apparatus for performing a decimal multiply operation.
2. Description of the Prior Art
Numerous techniques for multiplying two operands are known in the prior art. A common technique, since the multiplier and multiplicand may be in binary form, is to examine each multiplier bit in turn. A binary ONE results in an "add and shift" operation and a binary ZERO results in a "shift" operation to develop partial products. This form of multiplication required too many machine cycles for execution thereby reducing system throughput.
U.S. Pat. No. 3,293,419 assigned to the same assignee as the present invention discloses apparatus which decreases the time for performing the multiply operation by storing multiples of an operand. U.S. Pat. No. 3,641,331 also assigned to the same assignee as the present invention provided improved apparatus for generating and storing multiples of the operand. The storing of the multiple technique required extensive hardware.
U.S. Pat. No. 4,086,474 assigned to the same assignee as the present invention discloses apparatus using the "shift and add" technique which minimizes the time for the multiplication process particularly with respect to negative numbers. However, this technique is too slow for today's high-speed processing requirements and requires excessive hardware.
A typical multiplication technique is described in the IBM 1620 Central Processing Unit, Model 1, IBM 1620/1710 GA 26-5706-3, copyright 1962, 1964 by International Business Machines Corp. A multiplication table as well as the operands and product area are stored in main memory. This has the disadvantage of taking up a large area of main memory and restricting the multiplication speed to that of the main memory read write cycle.
It should be understood that the references cited herein are those of which the applicants are aware and are presented to acquaint the reader with the level of skill in the art and may not be the closest reference to the invention. No representation is made that any search has been conducted by the applicants.